#region Copyright notice and license

// Copyright 2015 gRPC authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#endregion

using System;
using Grpc.Core.Utils;

namespace Grpc.Core;

/// <summary>
/// Encapsulates the logic for serializing and deserializing messages.
/// </summary>
public class Marshaller<T>
{
    readonly Func<T, byte[]> serializer;
    readonly Func<byte[], T> deserializer;

    readonly Action<T, SerializationContext> contextualSerializer;
    readonly Func<DeserializationContext, T> contextualDeserializer;

    /// <summary>
    /// Initializes a new marshaller from simple serialize/deserialize functions.
    /// </summary>
    /// <param name="serializer">Function that will be used to serialize messages.</param>
    /// <param name="deserializer">Function that will be used to deserialize messages.</param>
    public Marshaller(Func<T, byte[]> serializer, Func<byte[], T> deserializer)
    {
        this.serializer = GrpcPreconditions.CheckNotNull(serializer, nameof(serializer));
        this.deserializer = GrpcPreconditions.CheckNotNull(deserializer, nameof(deserializer));
        // contextual serialization/deserialization is emulated to make the marshaller
        // usable with the grpc library (required for backward compatibility).
        this.contextualSerializer = EmulateContextualSerializer;
        this.contextualDeserializer = EmulateContextualDeserializer;
    }

    /// <summary>
    /// Initializes a new marshaller from serialize/deserialize fuctions that can access serialization and deserialization
    /// context. Compared to the simple serializer/deserializer functions, using the contextual version provides more
    /// flexibility and can lead to increased efficiency (and better performance).
    /// Note: This constructor is part of an experimental API that can change or be removed without any prior notice.
    /// </summary>
    /// <param name="serializer">Function that will be used to serialize messages.</param>
    /// <param name="deserializer">Function that will be used to deserialize messages.</param>
    public Marshaller(Action<T, SerializationContext> serializer, Func<DeserializationContext, T> deserializer)
    {
        this.contextualSerializer = GrpcPreconditions.CheckNotNull(serializer, nameof(serializer));
        this.contextualDeserializer = GrpcPreconditions.CheckNotNull(deserializer, nameof(deserializer));
        // gRPC only uses contextual serializer/deserializer internally, so emulating the legacy
        // (de)serializer is not necessary.
        this.serializer = (msg) => { throw new NotImplementedException(); };
        this.deserializer = (payload) => { throw new NotImplementedException(); };
    }

    /// <summary>
    /// Gets the serializer function.
    /// </summary>
    public Func<T, byte[]> Serializer => this.serializer;

    /// <summary>
    /// Gets the deserializer function.
    /// </summary>
    public Func<byte[], T> Deserializer => this.deserializer;

    /// <summary>
    /// Gets the serializer function.
    /// Note: experimental API that can change or be removed without any prior notice.
    /// </summary>
    public Action<T, SerializationContext> ContextualSerializer => this.contextualSerializer;

    /// <summary>
    /// Gets the serializer function.
    /// Note: experimental API that can change or be removed without any prior notice.
    /// </summary>
    public Func<DeserializationContext, T> ContextualDeserializer => this.contextualDeserializer;

    // for backward compatibility, emulate the contextual serializer using the simple one
    private void EmulateContextualSerializer(T message, SerializationContext context)
    {
        var payload = this.serializer(message);
        context.Complete(payload);
    }

    // for backward compatibility, emulate the contextual deserializer using the simple one
    private T EmulateContextualDeserializer(DeserializationContext context)
    {
        return this.deserializer(context.PayloadAsNewBuffer());
    }
}

/// <summary>
/// Utilities for creating marshallers.
/// </summary>
public static class Marshallers
{
    /// <summary>
    /// Creates a marshaller from specified serializer and deserializer.
    /// </summary>
    public static Marshaller<T> Create<T>(Func<T, byte[]> serializer, Func<byte[], T> deserializer)
    {
        return new Marshaller<T>(serializer, deserializer);
    }

    /// <summary>
    /// Creates a marshaller from specified contextual serializer and deserializer.
    /// Note: This method is part of an experimental API that can change or be removed without any prior notice.
    /// </summary>
    public static Marshaller<T> Create<T>(Action<T, SerializationContext> serializer, Func<DeserializationContext, T> deserializer)
    {
        return new Marshaller<T>(serializer, deserializer);
    }

    /// <summary>
    /// Returns a marshaller for <c>string</c> type. This is useful for testing.
    /// </summary>
    public static Marshaller<string> StringMarshaller
    {
        get
        {
            return new Marshaller<string>(System.Text.Encoding.UTF8.GetBytes,
                                          System.Text.Encoding.UTF8.GetString);
        }
    }
}
